Provided by: postgres-xc-client_1.1-2ubuntu2_amd64 
NAME
CREATE_FUNCTION - define a new function
SYNOPSIS
CREATE [ OR REPLACE ] FUNCTION
name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )
[ RETURNS rettype
| RETURNS TABLE ( column_name column_type [, ...] ) ]
{ LANGUAGE lang_name
| WINDOW
| IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
| [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
| COST execution_cost
| ROWS result_rows
| SET configuration_parameter { TO value | = value | FROM CURRENT }
| AS 'definition'
| AS 'obj_file', 'link_symbol'
} ...
[ WITH ( attribute [, ...] ) ]
DESCRIPTION
Note
Postgres-XC currently does not support creation of SQL functions containing utility statements. This
limitation is however enforced only when the GUC check_function_bodies is on. If SQL functions are
created after setting check_function_bodies to off, the behaviour of the function when executed is
un-defined. Other than this limitation the following description applies both to Postgres-XC and
PostgreSQL if not described explicitly.
CREATE FUNCTION defines a new function. CREATE OR REPLACE FUNCTION will either create a new function, or
replace an existing definition. To be able to define a function, the user must have the USAGE privilege
on the language.
If a schema name is included, then the function is created in the specified schema. Otherwise it is
created in the current schema. The name of the new function must not match any existing function with the
same input argument types in the same schema. However, functions of different argument types can share a
name (this is called overloading).
To replace the current definition of an existing function, use CREATE OR REPLACE FUNCTION. It is not
possible to change the name or argument types of a function this way (if you tried, you would actually be
creating a new, distinct function). Also, CREATE OR REPLACE FUNCTION will not let you change the return
type of an existing function. To do that, you must drop and recreate the function. (When using OUT
parameters, that means you cannot change the types of any OUT parameters except by dropping the
function.)
When CREATE OR REPLACE FUNCTION is used to replace an existing function, the ownership and permissions of
the function do not change. All other function properties are assigned the values specified or implied in
the command. You must own the function to replace it (this includes being a member of the owning role).
If you drop and then recreate a function, the new function is not the same entity as the old; you will
have to drop existing rules, views, triggers, etc. that refer to the old function. Use CREATE OR REPLACE
FUNCTION to change a function definition without breaking objects that refer to the function. Also, ALTER
FUNCTION can be used to change most of the auxiliary properties of an existing function.
The user that creates the function becomes the owner of the function.
To be able to create a function, you must have USAGE privilege on the argument types and the return type.
PARAMETERS
name
The name (optionally schema-qualified) of the function to create.
argmode
The mode of an argument: IN, OUT, INOUT, or VARIADIC. If omitted, the default is IN. Only OUT
arguments can follow a VARIADIC one. Also, OUT and INOUT arguments cannot be used together with the
RETURNS TABLE notation.
argname
The name of an argument. Some languages (currently only PL/pgSQL) let you use the name in the
function body. For other languages the name of an input argument is just extra documentation, so far
as the function itself is concerned; but you can use input argument names when calling a function to
improve readability (see Section 4.3, “Calling Functions”, in the documentation). In any case, the
name of an output argument is significant, because it defines the column name in the result row type.
(If you omit the name for an output argument, the system will choose a default column name.)
argtype
The data type(s) of the function's arguments (optionally schema-qualified), if any. The argument
types can be base, composite, or domain types, or can reference the type of a table column.
Depending on the implementation language it might also be allowed to specify “pseudotypes” such as
cstring. Pseudotypes indicate that the actual argument type is either incompletely specified, or
outside the set of ordinary SQL data types.
The type of a column is referenced by writing table_name.column_name%TYPE. Using this feature can
sometimes help make a function independent of changes to the definition of a table.
default_expr
An expression to be used as default value if the parameter is not specified. The expression has to be
coercible to the argument type of the parameter. Only input (including INOUT) parameters can have a
default value. All input parameters following a parameter with a default value must have default
values as well.
rettype
The return data type (optionally schema-qualified). The return type can be a base, composite, or
domain type, or can reference the type of a table column. Depending on the implementation language it
might also be allowed to specify “pseudotypes” such as cstring. If the function is not supposed to
return a value, specify void as the return type.
When there are OUT or INOUT parameters, the RETURNS clause can be omitted. If present, it must agree
with the result type implied by the output parameters: RECORD if there are multiple output
parameters, or the same type as the single output parameter.
The SETOF modifier indicates that the function will return a set of items, rather than a single item.
The type of a column is referenced by writing table_name.column_name%TYPE.
column_name
The name of an output column in the RETURNS TABLE syntax. This is effectively another way of
declaring a named OUT parameter, except that RETURNS TABLE also implies RETURNS SETOF.
column_type
The data type of an output column in the RETURNS TABLE syntax.
lang_name
The name of the language that the function is implemented in. Can be SQL, C, internal, or the name of
a user-defined procedural language. For backward compatibility, the name can be enclosed by single
quotes.
WINDOW
WINDOW indicates that the function is a window function rather than a plain function. This is
currently only useful for functions written in C. The WINDOW attribute cannot be changed when
replacing an existing function definition.
IMMUTABLE, STABLE, VOLATILE
These attributes inform the query optimizer about the behavior of the function. At most one choice
can be specified. If none of these appear, VOLATILE is the default assumption.
IMMUTABLE indicates that the function cannot modify the database and always returns the same result
when given the same argument values; that is, it does not do database lookups or otherwise use
information not directly present in its argument list. If this option is given, any call of the
function with all-constant arguments can be immediately replaced with the function value.
STABLE indicates that the function cannot modify the database, and that within a single table scan it
will consistently return the same result for the same argument values, but that its result could
change across SQL statements. This is the appropriate selection for functions whose results depend on
database lookups, parameter variables (such as the current time zone), etc. (It is inappropriate for
AFTER triggers that wish to query rows modified by the current command.) Also note that the
current_timestamp family of functions qualify as stable, since their values do not change within a
transaction.
VOLATILE indicates that the function value can change even within a single table scan, so no
optimizations can be made. Relatively few database functions are volatile in this sense; some
examples are random(), currval(), timeofday(). But note that any function that has side-effects must
be classified volatile, even if its result is quite predictable, to prevent calls from being
optimized away; an example is setval().
For additional details see Section 36.6, “Function Volatility Categories”, in the documentation.
LEAKPROOF
LEAKPROOF indicates that the function has no side effects. It reveals no information about its
arguments other than by its return value. For example, a function which throws an error message for
some argument values but not others, or which includes the argument values in any error message, is
not leakproof. The query planner may push leakproof functions (but not others) into views created
with the security_barrier option. See CREATE VIEW (CREATE_VIEW(7)) and Section 38.4, “Rules and
Privileges”, in the documentation. This option can only be set by the superuser.
CALLED ON NULL INPUT, RETURNS NULL ON NULL INPUT, STRICT
CALLED ON NULL INPUT (the default) indicates that the function will be called normally when some of
its arguments are null. It is then the function author's responsibility to check for null values if
necessary and respond appropriately.
RETURNS NULL ON NULL INPUT or STRICT indicates that the function always returns null whenever any of
its arguments are null. If this parameter is specified, the function is not executed when there are
null arguments; instead a null result is assumed automatically.
[EXTERNAL] SECURITY INVOKER, [EXTERNAL] SECURITY DEFINER
SECURITY INVOKER indicates that the function is to be executed with the privileges of the user that
calls it. That is the default. SECURITY DEFINER specifies that the function is to be executed with
the privileges of the user that created it.
The key word EXTERNAL is allowed for SQL conformance, but it is optional since, unlike in SQL, this
feature applies to all functions not only external ones.
execution_cost
A positive number giving the estimated execution cost for the function, in units of
cpu_operator_cost. If the function returns a set, this is the cost per returned row. If the cost is
not specified, 1 unit is assumed for C-language and internal functions, and 100 units for functions
in all other languages. Larger values cause the planner to try to avoid evaluating the function more
often than necessary.
result_rows
A positive number giving the estimated number of rows that the planner should expect the function to
return. This is only allowed when the function is declared to return a set. The default assumption is
1000 rows.
configuration_parameter, value
The SET clause causes the specified configuration parameter to be set to the specified value when the
function is entered, and then restored to its prior value when the function exits. SET FROM CURRENT
saves the session's current value of the parameter as the value to be applied when the function is
entered.
If a SET clause is attached to a function, then the effects of a SET LOCAL command executed inside
the function for the same variable are restricted to the function: the configuration parameter's
prior value is still restored at function exit. However, an ordinary SET command (without LOCAL)
overrides the SET clause, much as it would do for a previous SET LOCAL command: the effects of such a
command will persist after function exit, unless the current transaction is rolled back.
See SET(7) and Chapter 17, Coordinator and Datanode Configuration, in the documentation for more
information about allowed parameter names and values.
definition
A string constant defining the function; the meaning depends on the language. It can be an internal
function name, the path to an object file, an SQL command, or text in a procedural language.
It is often helpful to use dollar quoting (see Section 4.1.2.4, “Dollar-quoted String Constants”, in
the documentation) to write the function definition string, rather than the normal single quote
syntax. Without dollar quoting, any single quotes or backslashes in the function definition must be
escaped by doubling them.
obj_file, link_symbol
This form of the AS clause is used for dynamically loadable C language functions when the function
name in the C language source code is not the same as the name of the SQL function. The string
obj_file is the name of the file containing the dynamically loadable object, and link_symbol is the
function's link symbol, that is, the name of the function in the C language source code. If the link
symbol is omitted, it is assumed to be the same as the name of the SQL function being defined.
When repeated CREATE FUNCTION calls refer to the same object file, the file is only loaded once per
session. To unload and reload the file (perhaps during development), start a new session.
Note
The following description applies only to Postgres-XC
It is user's responsibility to deploy the file to all the servers where Coordinator or Datanode may
run.
attribute
The historical way to specify optional pieces of information about the function. The following
attributes can appear here:
isStrict
Equivalent to STRICT or RETURNS NULL ON NULL INPUT.
isCachable
isCachable is an obsolete equivalent of IMMUTABLE; it's still accepted for
backwards-compatibility reasons.
Attribute names are not case-sensitive.
Refer to Section 36.3, “User-defined Functions”, in the documentation for further information on writing
functions.
OVERLOADING
Postgres-XC allows function overloading; that is, the same name can be used for several different
functions so long as they have distinct input argument types. However, the C names of all functions must
be different, so you must give overloaded C functions different C names (for example, use the argument
types as part of the C names).
Two functions are considered the same if they have the same names and input argument types, ignoring any
OUT parameters. Thus for example these declarations conflict:
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, out text) ...
Functions that have different argument type lists will not be considered to conflict at creation time,
but if defaults are provided they might conflict in use. For example, consider
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, int default 42) ...
A call foo(10) will fail due to the ambiguity about which function should be called.
NOTES
The full SQL type syntax is allowed for input arguments and return value. However, some details of the
type specification (e.g., the precision field for type numeric) are the responsibility of the underlying
function implementation and are silently swallowed (i.e., not recognized or enforced) by the CREATE
FUNCTION command.
When replacing an existing function with CREATE OR REPLACE FUNCTION, there are restrictions on changing
parameter names. You cannot change the name already assigned to any input parameter (although you can add
names to parameters that had none before). If there is more than one output parameter, you cannot change
the names of the output parameters, because that would change the column names of the anonymous composite
type that describes the function's result. These restrictions are made to ensure that existing calls of
the function do not stop working when it is replaced.
If a function is declared STRICT with a VARIADIC argument, the strictness check tests that the variadic
array as a whole is non-null. The function will still be called if the array has null elements.
EXAMPLES
Here are some trivial examples to help you get started. For more information and examples, see Section
36.3, “User-defined Functions”, in the documentation.
CREATE FUNCTION add(integer, integer) RETURNS integer
AS 'select $1 + $2;'
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
Increment an integer, making use of an argument name, in PL/pgSQL:
CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
BEGIN
RETURN i + 1;
END;
$$ LANGUAGE plpgsql;
Return a record containing multiple output parameters:
CREATE FUNCTION dup(in int, out f1 int, out f2 text)
AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
LANGUAGE SQL;
SELECT * FROM dup(42);
You can do the same thing more verbosely with an explicitly named composite type:
CREATE TYPE dup_result AS (f1 int, f2 text);
CREATE FUNCTION dup(int) RETURNS dup_result
AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
LANGUAGE SQL;
SELECT * FROM dup(42);
Another way to return multiple columns is to use a TABLE function:
CREATE FUNCTION dup(int) RETURNS TABLE(f1 int, f2 text)
AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
LANGUAGE SQL;
SELECT * FROM dup(42);
However, a TABLE function is different from the preceding examples, because it actually returns a set of
records, not just one record.
WRITING SECURITY DEFINER FUNCTIONS SAFELY
Because a SECURITY DEFINER function is executed with the privileges of the user that created it, care is
needed to ensure that the function cannot be misused. For security, search_path should be set to exclude
any schemas writable by untrusted users. This prevents malicious users from creating objects that mask
objects used by the function. Particularly important in this regard is the temporary-table schema, which
is searched first by default, and is normally writable by anyone. A secure arrangement can be had by
forcing the temporary schema to be searched last. To do this, write pg_temp as the last entry in
search_path. This function illustrates safe usage:
CREATE FUNCTION check_password(uname TEXT, pass TEXT)
RETURNS BOOLEAN AS $$
DECLARE passed BOOLEAN;
BEGIN
SELECT (pwd = $2) INTO passed
FROM pwds
WHERE username = $1;
RETURN passed;
END;
$$ LANGUAGE plpgsql
SECURITY DEFINER
-- Set a secure search_path: trusted schema(s), then 'pg_temp'.
SET search_path = admin, pg_temp;
Another point to keep in mind is that by default, execute privilege is granted to PUBLIC for newly
created functions (see GRANT(7) for more information). Frequently you will wish to restrict use of a
security definer function to only some users. To do that, you must revoke the default PUBLIC privileges
and then grant execute privilege selectively. To avoid having a window where the new function is
accessible to all, create it and set the privileges within a single transaction. For example:
BEGIN;
CREATE FUNCTION check_password(uname TEXT, pass TEXT) ... SECURITY DEFINER;
REVOKE ALL ON FUNCTION check_password(uname TEXT, pass TEXT) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION check_password(uname TEXT, pass TEXT) TO admins;
COMMIT;
COMPATIBILITY
A CREATE FUNCTION command is defined in SQL:1999 and later. The Postgres-XC version is similar but not
fully compatible. The attributes are not portable, neither are the different available languages.
For compatibility with some other database systems, argmode can be written either before or after
argname. But only the first way is standard-compliant.
The SQL standard does not specify parameter defaults. The syntax with the DEFAULT key word is from
Oracle, and it is somewhat in the spirit of the standard: SQL/PSM uses it for variable default values.
The syntax with = is used in T-SQL and Firebird.
SEE ALSO
ALTER FUNCTION (ALTER_FUNCTION(7)), DROP FUNCTION (DROP_FUNCTION(7)), GRANT(7), LOAD(7), REVOKE(7),
createlang(1)